1. Technical Field
The present disclosure relates to a file producing method for producing an MP4 file.
2. Description of the Related Art
A file format used in a conventional optical disk is an MPEG2-TS (MPEG-2 Transport Stream) system specified by ISO/IEC 138181-1. Hereinafter, the MPEG2-TS system is simply referred to as MPEG2-TS. A file constructed by multiplexing a video stream, an audio stream, and a caption stream in an MPEG2-TS file format is recorded in the optical disk. Specifically, in the MPEG2-TS, each of the video stream, the audio stream, and the caption stream is multiplexed while divided into a plurality of 188-byte TS packets, and recorded in the optical disk. The MPEG2-TS is optimized for a medium, such as broadcasting and the optical disk, which transmits or records data sequentially read and processed. Accordingly, a stream is efficiently read, decrypted, and played back even by a consumer product having a relatively small buffer capacity.
On the other hand, a nowadays file format that is increasingly used in content distribution through a network is an MP4 system specified by ISO/IEC 14496-12. Hereinafter, the MP4 system is simply referred to as MP4. The MP4 adopts an extremely flexible data structure on the assumption of application to a randomly accessible medium such as an HDD (Hard Disk Drive) and a flash memory. In a general use form of the MP4, the stream such as the video stream, the audio stream, and the caption stream is divided in units of several-second fragments, and the fragments are sequentially arrayed to construct one file.
From a viewpoint of bit unit cost, it is considered that frequently the optical disk is used as the medium to distribute high-quality content, such as 4K content, which is expected to grow. On the other hand, although a smartphone and a tablet do not include an optical disk drive, the smartphone and the tablet are used as a terminal receiving and playing back the content distribution in the network by utilizing high portability, a large screen size, and a finer image. For this reason, the smartphone and the tablet have many functions and pieces of processing compatible with the MP4, and the adoption of the function and processing compatible with the MPEG2-TS is not progressing very much.
Sometimes the file format of the content of an MPEG2-TS file distributed as the optical disk is converted into the MP4 when the content is copied in the smartphone and the tablet (for example, see PTL 1). An MP4 file that is of a file of the MP4 is produced by the conversion.